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GPS signal blockage can be experienced in many environments a vehicle may encounter; a forested road, the urban jungle, a tunnel, road spaghetti – you get the picture. Inertial sensors complement GPS well, potentially bridging the gaps in GPS coverage and provide vehicle attitude information as a bonus. But there is a catch, the data streams from a GPS receiver and inertial sensors are independent and must be fused together to generate a useful stream of navigation (position, velocity, and attitude) data. In this article the hardware and software algorithms that have been developed at the University of New South Wales to do this fusing operation are presented along with an example of the capabilities of the system. The article concludes with a look at some applications presently being explored and ideas for future work. The complimentary nature of GPS and Inertial Navigation System (INS) is well known; GPS provides absolute XYZ coordinates at a low data rate, while INS essentially provides changes in XYZ (and attitude) at a high data rate. While GPS can suffer loss of satellite signals that can lead to no XYZ at all, INS just keeps on going but will drift as errors compound. So it’s a happy marriage; GPS can bound the INS errors and INS can fill the gaps between GPS fixes. Broadly speaking there are four parts to our GPS/INS system; the sensors, the synchronization component, the integration / fusion component and data output. The system can operate in real-time or post-processing mode, the data fusion algorithms for both modes are essentially the same. In the real-time mode the algorithms run on an embedded processor on the prototype hardware device. In the post-process mode, the algorithms run on a PC. The hardware and the system components will be detailed shortly, but first lets see what the system is capable of.